Speaker
Description
Understanding charge carrier dynamics at p–n heterojunctions is essential for designing high-efficiency photo-catalysts. Here, we investigate ultrafast charge transfer pathways in a layered CuO/TiO2 heterostructure using time-resolved soft X-ray absorption spectroscopy (tr-XAS) with PAL-XFEL for probing transient electronic structure with elemental and orbital sensitivity.
By tracking transient signals at the O K-, Cu L3-, and Ti L2-edges, we identify a pronounced hole accumulation in the CuO valence band on a nanosecond timescale. In contrast, the photo excited electron exhibits a multistep evolution across the junction. Immediately after excitation, electrons in the TiO2 conduction band diffuse into the CuO conduction band within approximately 150 ps. Subsequently, these electrons drift back toward the TiO2 conduction band within about 800 ps, consistent with favorable energetic alignment (lower-lying TiO2 CB) and the larger electron population reservoir in TiO2.
Notably, electrons residing in TiO2 persist up to ~3500 ps, attributable to trapping into deep trap states. This spatial charge separation, driven by the built-in electric field at the p–n interface, effectively suppresses electron–hole recombination and stabilizes long-lived carriers. These findings highlight the power of element-resolved ultrafast X-ray spectroscopy for disentangling interfacial carrier pathways and motivate future XFEL based femtosecond-to-nanosecond studies of heterojunction photo catalysts.
| Scientific Topics | Solid State Physics |
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